1. Field of the Art
The present invention relates to Ziegler polymerization of olefins. More particularly, the present invention is concerned with Ziegler polymerization of olefins, typically .alpha.-olefins of at least 3 carbon atoms, characterized by, among others, the solid catalyst components comprising a transition metal in Ziegler catalysts and the polymerization temperature used which is no lower than 150.degree. C.
Use of the solid catalyst component in accordance with the present invention in Ziegler catalysts as the transition metal component at the temperature will make it possible to produce polymers endowed with improved stereoregularity and broadened molecular weight distribution.
2. Background of the Invention
The catalysts heretofore proposed for the polymerization of olefins comprising a solid catalyst component containing titanium, magnesium and a halogen as the essential components and an organoaluminum compound (and an electron donor, if desired) have produced highly stereoregular polymers.
Such prior art catalysts are such that their catalyst activity may often be found at a polymerization temperature of 90.degree. C. or lower, preferably 80.degree. C. or lower.
It has been known in the art that ethylene polymerizes at such a higher temperature as 150.degree. to 250.degree. C. similarly at a temperature of 70.degree. to 90.degree. C. and that polymerization of ethylene at such a higher temperature is known to have such preferable characteristics that the polyethylenes produced have a narrower molecular weight distribution or copolymerizability of ethylene with another monomer is improved.
It has also been known in the art that propylene will not produce polymers endowed with acceptably high stereoregularity when it is polymerized at such a high temperature as 150.degree. C. or higher. One possible reason therefor may be such that the solid structure comprising the titanium component capable of polymerizing propylene into polymers of high stereoregularity is destroyed at a temperature no lower than 150.degree. C., the titanium component is agglomerated or excessively reduced by the organoaluminum component as a co-catalyst, or, when an electron donor is used during polymerization as what is called "outside electron donor", it reacts so strongly with the titanium component or with the organoaluminum component at such a higher temperature that the catalyst activity is thus lowered.
Catalysts which are capable of producing highly stereoregular polymers at such a high temperature as no lower than 150.degree. C. have, to the best of the present inventors, not been proposed.
It has also been known to use as an organoaluminum component in the Ziegler catalysts organoaluminum compounds which contain a halogen atom. The halogen atom may have such a problem due to its inherent corrosive nature that polyolefins produced therewith can corrode or rust processing machines for the polymers. An organoaluminum component in Ziegler catalysts which is free from a halogen contained therein has heretofore been desired.